1. Field of the Invention
The present invention relates to an ink jet cartridge and, in particular, to a valve design applicable to an ink jet cartridge for controlling the ink flow between the ink reservoir and the ink chamber and adjusting the air pressure in the ink chamber to keep the pressure in the ink chamber within the allowed range as the ink gradually gets depleted or the environmental pressure changes.
2. Related Art
In ink jet printing, it is common to use ink control methods such as the heat bubble or piezoelectric wave ink jet cartridge to control the ink output. The print head of the heat bubble ink jet cartridge contains a thin film resistor which can instantaneously vaporize the tiny ink droplet after being heated and the vaporized ink droplet rapidly expand to pass the ejection nozzle of the print head and print on the paper. Although it can effectively get ink from the ink reservoir of the ink jet cartridge and spray ink, yet it still requires an extra control mechanism to prevent it from leaking while it is not working.
This control mechanism usually prevents the print head from leaking by providing the print head with a slight back pressure due to the partial vacuum in the ink reservoir. The back pressure is expressed in positive values. Therefore, an increase in the value of the back pressure indicates a better vacuum in the reservoir.
In the design of an ink jet cartridge, one usually needs to consider the following factors:
1. The pressure between the ink reservoir and the environment has to be balanced by the adjustment of the back pressure, which, however, can not be so large that the print head can not overcome the back pressure to jet ink and provide a proper ink supply or the size of the ink droplet it spreads out changes so much to deteriorate the printing quality. PA0 2. The back pressure in the ink reservoir has to be able to be adjusted according to the environmental pressure change and to be kept within the allowed range. For example, when the environmental pressure decreases, the back pressure has to be larger so that the ink will not leak out of the print head. PA0 3. The operating effect of the ink reservoir also has an effect on the back pressure in the ink reservoir. For example, the continuous consumption of the ink in the ink reservoir will raise the back pressure in the ink reservoir. Eventually the large back pressure will prohibit the print head from spreading out ink if it is not properly adjusted.
Currently, the adjustment of the back pressure in the ink reservoir is achieved by a device called accumulator in the ink reservoir, which in general is an elastic air bag. This device is designed to change, via the action of the accumulator with its volume varying between its maximum and minimum, the volume of the ink reservoir and thus to adjust the back pressure.
Referring to FIG. 1, which shows the structure of the ink jet cartridge 1 that is equipped with an accumulator 20 as disclosed in the U.S. Pat. No. 5,409,134. The ink jet cartidge 1 comprises:
an ink reservoir 10, which is enclosed by a case 11; PA1 a print head 30, which is placed at the bottom of the ink reservoir 10 and via which the ink 40 in the ink reservoir 10 can be printed on the paper; PA1 an accumulator 20 placed within the ink reservoir 10, which comprises: PA1 a plunger chamber, which includes: an atmospheric opening connecting to the atmosphere, an ink inlet connecting to a orifice on the ink reservoir, an ink outlet connecting to the ink chamber, and a feedback opening connecting to the ink chamber; and PA1 a plunger, which is placed between the atmospheric opening and the feedback opening within the plunger chamber to cover the ink inlet and the ink outlet and can be moved by the pressure difference between the environment and the ink chamber to determine whether the ink reservoir and the ink chamber are connected or not; wherein the plunger further comprises a channel connecting the ink inlet and ink outlet for the ink to flow from the ink reservoir into the ink chamber.
a spring 21a, 21b; PA2 an air bag 22a, 22b, which is encompassed by two thin movable plates 23, 24; PA2 a support 25, which connects to the air bag 22a, 22b and provide a venthole 12 for the air to enter the air bag 22a, 22b.
The support 25 is installed with a wheel net 26, and the air bag 22a, 22b along with the spring 21a, 21b are fixed onto the case 11 by a positioning pin 27. In addition, a ventilating duct 28 is placed between the movable plates 23, 24 for the air to flow through the venthole 12 and enter the air bag 22a, 22b. After filling up the ink reservoir 10 with the ink 40, the ink reservoir 10 will obtain its minimal back pressure under the action of the accumulator 20 and therefore will not allow the ink 40 to leak out of the print head 30 in the stand-by state.
When printing, the ink 40 will be gradually depleted and increase the vacuum and thus the back pressure within the ink reservoir 10. At this moment, the air will flow through the ventilating duct 28 into the air bag 22a, 22b and inflate the air bag 22a, 22b, thus the space in the ink reservoir decreases and balance the back pressure increase in the ink reservoir 10.
Referring to FIG. 2. When the environmental pressure decreases (for example, in the airfreight), the spring 21a, 21b will press upon and contract the air bag 22a, 22b (the air within is then squeezed out by the external force) so that the space in the ink reservoir 10 increases. Therefore, the back pressure in the ink reservoir 10 will not decrease as the environmental pressure decreases, and the ink 40 will not leak out of the print head 30.